1. Field of the Invention
The present invention relates to a discharge tube, and more particularly to a technology to drive a discharge tube efficiently and stably. The present invention further relates to the control of a discharge lamp.
2. Description of the Related Art
A discharge lamp having a discharge tube is used as a light source for a projector or other device. This discharge tube may be driven by a single-phase power supply (e.g. JP06-325735A) or a multiple-phase power supply (e.g. JP64-86442A).
A discharge lamp of the conventional art commonly has two electrodes. A discharge lamp control device generally causes discharge lamp illumination by impressing voltage to the two electrodes and creating an electric discharge between the two electrodes. When AC voltage is impressed to this conventional single-phase-driven discharge lamp, the discharge lamp becomes a light source that repeatedly alternates between an illuminated state and a non-illuminated state.
The above conventional discharge tube may fluctuate in its discharge characteristics, and offers insufficient discharge efficiency and stability of output intensity. Furthermore, as a result of the electrodes or the like residing in the light transmission path, the problems of light loss and poor light transmission efficiency may occur.
These problems are not limited to a discharge tube in a discharge lamp used as a projector light source, but are common to general discharge tubes.
In addition, various problems arise due to the fact that the discharge lamp is a light source that repeatedly blinks on and off. For example, where this type of discharge lamp is used in a display device such as a projector, flicker caused by interference between the light source illumination frequency and the display device drive frequency occurs. Furthermore, where this type of discharge lamp that repeatedly blinks on and off is used as an illumination device, flicker caused by interference with the light source illumination frequency of a different light source in the area may occur. Moreover, the discharge frequency may cause stress on the eyes and brain.
It has been considered to impress DC voltage to the electrodes in order to illuminate the discharge lamp. However, if DC voltage is impressed, the load on the electrodes becomes large, thereby shortening their life span.